High-resolution terahertz wave concentration module, scattered light detection module, and high-resolution inspection apparatus using terahertz bessel beam

ABSTRACT

According to one embodiment of the present invention, a terahertz wave concentrating module can comprise: a first lens for changing a terahertz wave, which is emitted while a terahertz Bessel beam penetrates an object to be inspected, so as to have a small angle; and a second lens for concentrating, on a detector, the terahertz wave having passed through the first lens.

This application is a divisional of U.S. patent application Ser. No.16/344,494 filed Apr. 24, 2019, now U.S. Pat. No. 10,648,864 issued May12, 2020, which is a National Stage completion of PCT/KR2016/013564filed Nov. 23, 2016, which claims priority from Korean patentapplication serial nos. 10-2016-0156244 filed Nov. 23, 2016,10-2016-0144582 filed Nov. 1, 2016 and 10-2016-0144573 filed Nov. 1,2016.

TECHNICAL FIELD

The present invention relates to a technique of inspecting a targetobject to be inspected (or an inspection target object) by anondestructive method using a terahertz wave, and more particularly, toa high-resolution terahertz wave concentrating module having a highresolution below a wavelength beyond a diffraction limit.

Further, the present invention relates to a scattered light detectionmodule which forms a ring beam using a Bessel beam and detects scatteredlight which is reflected from an inspection target object or transmittedthrough the inspection target object when the inspection target objectis inspected using the formed ring beam, thus enhancing contrast.

In addition, the present invention relates to a high-resolutioninspection apparatus using a terahertz Bessel beam, which recognizes ashape of an object using a scanner and synchronizes an optical head anda concentrating head according to the recognized shape of the object.

NATIONAL RESEARCH AND DEVELOPMENT PROJECT SUPPORTING PRESENT INVENTION

[Project No.] ER160200-01

[Ministry Name] Ministry of Science, ICT and Future Planning

[Research Management Specialist Agency] Korea Food Research Institute

[Research Title] Main Work of Korea Food Research Institute

[Research Project Title] Development of Terahertz High-ResolutionImaging Technique For Detecting Foreign Matter

[Contribution Rate] 1/1

[Managing Department] Korea Food Research Institute

[Research term] Apr. 1, 2016 to Dec. 31, 2017

BACKGROUND ART

An imaging method is generally used to inspect objects or substances ina non-destructive manner. Two methods, i.e., an image detection methodusing a continuous output light source and an image detection methodusing a spectroscopic method are mainstream imaging methods. Thesemethods have advantages and disadvantages, but the image detectionmethod using a continuous output light source is widely used in fieldsrequiring relatively high power such as a transmission image.

A terahertz wave is widely used in the field of qualitatively checkingfor a hidden object or substance in a non-destructive manner due tovarious excellent properties such as transmissivity with respect tomaterials, possibility of qualitative checking, safety to a living body,and the like.

Accordingly, the terahertz wave has recently been utilized in variousfields such as a search device in an airport or a security facility, aquality inspection device in a food or pharmaceutical company, asemiconductor inspection device, an engineering plastic inspectiondevice, and the like.

The use of terahertz waves in production sites has increased, and muchimprovement has been made by continuous research in terms of majorperformance indices such as detection resolution, detection rate,detection area, and the like.

In the past, in order to obtain a terahertz wave transmission image,only one lens was used to concentrate a terahertz wave which is radiatedafter being transmitted through an object. In this case, if an apicalangle of an axicon lens forming a Bessel beam is regulated to be smallso as to make a beam size of the terahertz wave focused on an inspectiontarget object be less than a wavelength, a terahertz Bessel beam passingthrough the inspection target object is radiated at a large angle and isnot entirely concentrated to a detection unit. Thus, light concentrationcharacteristics significantly deteriorates and a signal per noise ratio(SNR) of an inspection device is drastically degraded, and thus, anormal image cannot be obtained.

Further, it is difficult to obtain a clear image of a transparentinspection target object. Therefore, there is a need for research anddevelopment of a method for enhancing the contrast of a transparentinspection target object with little loss of a terahertz wave.

In addition, there is a problem in that a high resolution image cannotbe obtained because a depth of focus of the Bessel beam does not reachan end portion of the inspection target object.

Further, if the inspection target object contains a large amount ofwater, a proportion of a terahertz wave transmitted through theinspection target object is drastically lowered due to the properties ofterahertz waves being easily absorbed by moisture. As a result, thedetecting unit cannot correctly inspect the inspection target objectbecause a signal of the detected terahertz wave is weak.

The related art of the present invention is disclosed in Korean PatentRegistration No. 10-1392311.

DISCLOSURE Technical Problem

An aspect of the present invention provides a high-resolution terahertzwave concentrating module capable of increasing high resolution byincreasing concentration efficiency of a terahertz Bessel beamtransmitted through an inspection target object.

Another aspect of the present invention provides a scattered lightdetection module capable of increasing contrast for a transparentinspection target object by forming a ring beam without loss of aterahertz wave.

Another aspect of the present invention provides a high resolutioninspection apparatus using a terahertz Bessel beam, in which an opticalhead moves along the contour of an inspection target object as much aspossible according to a shape of the inspection target object so that adepth of focus of a Bessel beam may reach the end of the inspectiontarget object.

Another aspect of the present invention provides a high-resolutioninspection apparatus using a terahertz Bessel beam, which inspects aninspection target object containing moisture using a terahertz wave byrapidly cooling the inspection target object, so that the terahertz wavemay easily be transmitted through the inspection target object.

Other objects and advantages of the present invention may be understoodby the following descriptions and become apparent by the embodiments ofthe present invention. Also, it may be easily understood that theobjects and advantages of the present invention are realized by meansand combinations demonstrated in claims.

Technical Solution

According to an aspect of the present invention, there is provided ahigh resolution inspection apparatus using a Bessel beam, including: ascanner scanning a shape of an inspection target object; a terahertzwave optical head generating a terahertz wave and irradiating theinspection target object with the generated terahertz wave; a terahertzwave concentrating head detecting the terahertz wave transmitted throughthe inspection target object; a first transfer unit moving the terahertzwave optical head according to the scanned shape of the inspectiontarget object; and a second transfer unit moving the terahertz waveconcentrating head in the same manner as the optical head insynchronization with the first transfer unit.

The first transfer unit may move the terahertz wave optical head tomaintain a predetermined distance from the inspection target object onthe basis of a thickness of the scanned inspection target object so thatthe inspection target object is placed within a depth of focus of thegenerated terahertz wave.

The high resolution inspection apparatus may further include: a rapidcooling device maintaining the inspection target object in a lowtemperature state, wherein the terahertz wave optical head and theterahertz wave concentrating head may be disposed on opposing sides ofthe rapid cooling device so as to be spaced apart from each other.

The rapid cooling device may be configured as a housing including awindow allowing the generated terahertz wave to be transmittedtherethrough.

The high resolution inspection apparatus may further include: adefrosting device disposed in a rear stage of the rapid cooling deviceand defrosting the inspection target object.

According to another aspect of the present invention, there is provideda high resolution inspection apparatus using a Bessel beam, including: aterahertz wave generating unit generating a terahertz wave; a Besselbeam forming unit forming a terahertz Bessel beam at the inspectiontarget object using the terahertz wave incident from the terahertz wavegenerating unit; a first lens changing an angle of the terahertz waveradiated when the terahertz Bessel beam is transmitted through theinspection target object, to be smaller; a second lens concentrating theterahertz wave passing through the first lens to a detection unit; and aterahertz wave detection unit detecting the terahertz wave concentratedby the second lens.

The Bessel beam forming unit may be a first axicon lens having an apicalangle at which a diameter of the terahertz Bessel beam is smaller than awavelength of the terahertz wave generated by the terahertz wavegenerating unit.

The first lens may be a second axicon lens arranged to be symmetrical tothe first axicon lens with respect to the inspection target object.

The second axicon lens may have an apical angle having the same size asthe first axicon lens.

The high resolution inspection apparatus may further include: an anglechanging unit changing an angle of the terahertz wave incident from theterahertz wave generating unit to be smaller and to enter the Besselbeam forming unit.

The angle changing unit may be a first convex lens changing the angle ofthe terahertz wave incident from the terahertz wave generating unit tobe smaller and the second lens may be a second convex lens arranged tobe symmetrical to the first convex lens with respect to the inspectiontarget object.

The second lens may be a third axicon lens having the same shape as thesecond axicon lens and arranged to be symmetrical to the second axiconlens with respect to an axis perpendicular to an optical axis.

The first lens may be a third convex lens changing an angle of theterahertz wave radiated when the terahertz Bessel beam is transmittedthrough the inspection target object.

The second lens may be a fourth convex lens arranged to be symmetricalto the third convex lens with respect to the axis perpendicular to theoptical axis.

According to another aspect of the present invention, there is provideda high-resolution terahertz wave concentrating module, including: afirst lens changing an angle of a terahertz wave radiated when aterahertz Bessel beam is transmitted through an inspection targetobject, to be smaller; and a second lens concentrating the terahertzwave passing through the first lens to a terahertz wave detector.

The first lens may be a second axicon lens forming the terahertz Besselbeam and arranged to be symmetrical to a first axicon lens having anapical angle at which a diameter of the terahertz Bessel beam is smallerthan a wavelength of the terahertz wave generated by the terahertz wavegenerating unit with respect to the inspection target object.

The second axicon lens may have an apical angle having the same size asthe first axicon lens.

The second lens may be a second convex lens arranged to be symmetricalto a first convex lens changing an angle of the terahertz wave incidentfrom the terahertz wave generating unit, to be smaller with respect tothe inspection target object.

The second lens may have the same shape as the second axicon lens andmay be arranged to be symmetrical to the second axicon lens with respectto an axis perpendicular to an optical axis.

The first lens may be a third convex lens changing an angle of theterahertz wave radiated when the terahertz Bessel beam is transmittedthrough the inspection target object.

The second lens may be a fourth convex lens arranged to be symmetricalto the third convex lens with respect to the axis perpendicular to theoptical axis.

According to another aspect of the present invention, there is provideda high resolution inspection apparatus using a terahertz Bessel beam,including: a terahertz wave generating unit generating a terahertz wave;a Bessel beam forming unit generating a terahertz Bessel beam using theterahertz wave incident from the terahertz wave generating unit; a ringbeam forming unit forming a ring beam using the terahertz Bessel beamand concentrating the formed ring beam to an inspection target object; ascattered light detecting unit detecting scattered light generated fromthe inspection target object; and a ring beam detecting unit detecting aring beam transmitted through the inspection target object.

The ring beam forming unit may include a third lens forming a ring beamand concentrating the formed ring beam to the inspection target object.

The scattered light detecting unit may include a reflected scatteredlight detecting unit provided inside the third lens and detectingscattered light reflected from the inspection target object.

The reflected scattered light detecting unit may be provided inside aring beam exiting from the third lens.

The scattered light detecting unit may include a transmitted scatteredlight detecting unit detecting scattered light transmitted from theinspection target object.

The transmitted scattered light detecting may be arranged inside a ringbeam incident from the third lens.

The third lens may include a path changing unit changing a path of thescattered light reflected from the inspection target object, and thereflected scattered light detecting unit may detect scattered lightincident from the path changing unit.

The ring beam forming unit may include a fourth lens changing an angleof the terahertz Bessel beam incident from the Bessel beam forming unitto be smaller and to enter the third lens.

The Bessel beam forming unit may be a fourth axicon lens having anapical angle at which a diameter of the terahertz Bessel beam is smallerthan a wavelength of the terahertz wave generated by the terahertz wavegenerating unit.

The fourth lens may be a fifth axicon lens arranged to be symmetrical tothe fourth axicon lens with respect to the inspection target object.

The fifth axicon lens may have an apical angle having the same size asthe fourth axicon lens.

The high resolution inspection apparatus may further include: an anglechanging unit changing an angle of the terahertz wave incident from theterahertz wave generating unit to be smaller and incident on the Besselbeam forming unit.

The angle changing unit may be a fifth convex lens changing the angle ofthe terahertz wave incident from the terahertz wave generating unit, tobe smaller, and the third lens may be a sixth convex lens arranged to besymmetrical to the fifth convex lens with respect to the inspectiontarget object.

The third lens may be a sixth axicon lens having the same shape as thefifth axicon lens and arranged to be symmetrical to the fifth axiconlens with respect to an axis perpendicular to an optical axis.

The fourth lens may be a seventh convex lens changing an angle of theterahertz wave radiated when the terahertz Bessel beam is transmittedthrough the inspection target object.

The fourth lens may be an eighth convex lens arranged to be symmetricalto the seventh convex lens with respect to the axis perpendicular to theoptical axis.

According to another aspect of the present invention, there is provideda scattered light detection module, including: a ring beam forming unitforming a ring beam using the terahertz Bessel beam and concentratingthe formed ring beam to an inspection target object; and a scatteredlight detecting unit detecting scattered light generated from theinspection target object.

The ring beam forming unit may include a third lens forming a ring beamand concentrating the formed ring beam to the inspection target object.

The scattered light detecting unit may include a reflected scatteredlight detecting unit provided inside the ring beam exiting from thethird lens and detecting scattered light reflected from the inspectiontarget object.

The scattered light detecting unit may include a transmitted scatteredlight detecting unit arranged inside a ring beam incident from the thirdlens and detecting scattered light transmitted from the inspectiontarget object.

The third lens may include a path changing unit changing a path of thescattered light reflected from the inspection target object, and thereflected scattered light detecting unit may detect scattered lightincident from the path changing unit.

Advantageous Effects

According to the disclosure, since the terahertz wave penetrating aninspection target object is concentrated substantially without loss,concentration efficiency may be increased.

Further, a clear image may be obtained by increasing resolution byregulating a diameter of the terahertz wave beam focused on aninspection target object to be equal to or less than a wavelength of theterahertz wave.

Further, a ring beam may be formed without loss of the terahertz wave,so that the contrast of a transparent inspection target object may beincreased.

Further, the contrast of a transparent inspection target object may beincreased by detecting scattered light generated from the inspectiontarget object.

Further, since the scattered light detecting unit is disposed inside thegenerated ring beam, a separate space due to an addition of thescattered light detecting unit is not required, thereby achievingminiaturization.

Also, although the apical angle of the axicon of the Bessel beam formingunit is reduced to realize high resolution, a high resolution image maybe obtained by reducing the diameter of the ring beam generated usingtwo lenses of the ring beam forming unit.

Further, since the optical head moves along the contour of an inspectiontarget object as much as possible according to the shape of theinspection target object, the inspection target object may be positionedwithin the depth of focus of the Bessel beam, whereby a cleartransparent image may be obtained.

Further, since an inspection target object containing moisture israpidly cooled and inspected using a terahertz wave, the terahertz wavemay easily penetrate the inspection target object.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block view of a high resolution inspection apparatus using aterahertz Bessel beam according to an embodiment of the presentinvention.

FIG. 2 is a view specifically illustrating a high resolution inspectionapparatus using the terahertz Bessel beam of FIG. 1.

FIG. 3 is a view illustrating a high resolution inspection apparatususing a terahertz Bessel beam according to another embodiment of thepresent invention.

FIG. 4 is a view illustrating a high resolution inspection apparatususing a Bessel beam according to another embodiment of the presentinvention.

FIG. 5 is a view illustrating a Bessel beam forming unit according to anembodiment of the present invention.

FIG. 6 is a view illustrating a calculation of a diameter of a terahertzwave beam focused on different apical angles using Equation 4.

FIGS. 7 and 8 are views illustrating an inspection apparatus forconcentrating light using a single lens.

FIG. 9 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 4 according to a first embodiment.

FIG. 10 is a view illustrating the high-resolution inspection apparatusof FIG. 4 according to a second embodiment.

FIG. 11 is a view illustrating the high-resolution inspection apparatusof FIG. 4 according to a third embodiment.

FIGS. 12 and 13 are transmission images obtained by measuring aninspection target object using the apparatuses of FIGS. 8 to 11.

FIG. 14 is a view illustrating a high resolution inspection apparatususing a terahertz Bessel beam according to another embodiment of thepresent invention.

FIG. 15 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a firstembodiment.

FIG. 16 is a view illustrating a ring beam forming unit 1540 of FIG. 15.

FIG. 17 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a secondembodiment.

FIG. 18 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a thirdembodiment.

FIG. 19 is a view illustrating the high resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a fourthembodiment.

FIG. 20 is a view illustrating the high resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a fifthembodiment.

FIG. 21 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a sixthembodiment.

FIG. 22 is a view illustrating the high resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a seventhembodiment.

FIG. 23 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to an eighthembodiment.

BEST MODES

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

FIG. 1 is a view illustrating a high resolution inspection apparatususing a terahertz Bessel beam according to an embodiment of the presentinvention.

Referring to FIG. 1, a high resolution inspection apparatus 100 using aBessel beam includes a scanner 110, a terahertz wave optical head 120,an inspection target object 130, a terahertz wave concentrating head140, a first transfer unit 150, and a second transfer unit 160.

The scanner 110 may scan a shape of an inspection target object.

The terahertz wave optical head 120 may generate a terahertz wave andirradiate the generated terahertz wave to the inspection target object130.

The terahertz wave concentrating head 140 may detect a terahertz wavetransmitted through the inspection target object 130.

The first transfer unit 150 may move the terahertz wave optical head 120according to the shape of the inspection target object scanned by thescanner 110. The first transfer unit 150 may move the terahertz waveoptical head 120 in a direction to a two-dimensional plane and in adirection perpendicular to the two-dimensional plane.

For example, in order to place the inspection target object 130 within adepth of focus of the terahertz wave generated by the terahertz waveoptical head 120, the first transfer unit 150 may move the terahertzwave optical head 120 such that the terahertz wave optical head 120 andthe inspection target object 130 are maintained at a predetermineddistance on the basis of a thickness of the scanned inspection targetobject 130.

Specifically, assuming that the inspection target object has a portionhaving a thickness A and a portion having a thickness B, the firsttransfer unit 150 may move the optical head 120 by X in a verticaldirection when the portion having the thickness A is scanned. Also, whenthe portion having the thickness B is scanned, the first transfer unit150 may move the optical head 120 by Y in the vertical direction.

Accordingly, the first transfer unit 150 may move the optical head 120along the contour of the inspection target object 130 as much aspossible so that the inspection target object is positioned within thedepth of focus of the Bessel beam to obtain a clear transmission image.

The second transfer unit 160 may be synchronized with the first transferunit 150 to move the terahertz wave concentrating head 140 in the samemanner as the terahertz wave optical head 120. Thus, the first transferunit 150 and the second transfer unit 160 may cause the terahertz waveoptical head 120 and the terahertz wave concentrating head 140 to bealigned.

FIG. 2 is a view specifically illustrating the high resolutioninspection apparatus using a terahertz Bessel beam of FIG. 1.

Referring to FIG. 2, the high resolution inspection apparatus 100 usinga Bessel beam includes the scanner 110, the terahertz wave optical head120, the inspection target object 130, the terahertz wave concentratinghead 140, the first transfer unit 150, and the second transfer unit 160.

The scanner 110 may scan the shape of the inspection target object. Thescanner 110 may be disposed in a separate frame or may be disposedintegrally in front of the terahertz wave optical head 120.

The terahertz wave optical head 120 generates a terahertz wave andirradiates the generated terahertz wave to the inspection target object130.

The first transfer unit 150 may be mechanically coupled to the terahertzwave optical head 120. The first transfer unit 150 may move theterahertz wave optical head 120 according to the shape of the inspectiontarget object scanned by the scanner 110. The first transfer unit 150may move the terahertz wave optical head 120 in the direction to thetwo-dimensional plane and in the direction perpendicular to thetwo-dimensional plane.

The inspection target object 130 may be placed on a conveyor belt andmay be moved from the scanner 110 toward the terahertz wave optical head120. The inspection target object 130 may be moved by the conveyor beltor the like, as in the present embodiment, or may be fixed to bedisposed at a specific position.

The terahertz wave concentrating head 140 may detect a terahertz wavetransmitted through the inspection target object 130.

The second transfer unit 160 may be synchronized with the first transferunit 150 to move the terahertz wave concentrating head 140 in the samemanner as the terahertz wave optical head 120.

The first transfer unit 150 and the second transfer unit 160 may causethe terahertz wave optical head 120 and the terahertz wave concentratinghead 140 to be aligned.

The present embodiment merely provides the structure for helpingunderstand the shape of the high resolution inspection apparatus using aterahertz Bessel beam, and the high resolution inspection apparatususing a terahertz Bessel beam may be realized as various types ofstructures.

FIG. 3 is a view illustrating a high resolution inspection apparatususing a terahertz Bessel beam according to another embodiment of thepresent invention.

Referring to FIG. 3, the high resolution inspection apparatus using aBessel beam includes the terahertz wave optical head 120, the inspectiontarget object 130, the terahertz wave concentrating head 140, the firsttransfer unit 150, the second transfer unit 160, a rapid cooling device300, and a defrosting device 320.

The terahertz wave optical head 120, the inspection target object 130,the terahertz wave concentrating head 140, the first transfer unit 150,and the second transfer unit 160 are the same as those of FIG. 1, andthus, a redundant description thereof will be omitted.

The terahertz wave optical head 120 and the terahertz wave concentratinghead 140 may be disposed on opposing sides of the rapid cooling device300 so as to be spaced apart from each other.

The rapid cooling device 300 may maintain the inspection target object130 at a low temperature. For example, the rapid cooling device 300 maycool the inspection target object 130 to a solid state. Since theinspection target object 130 is maintained at a low temperature ormaintained in a solid state, a rate of absorption of the terahertz waveinto the inspection target object 130 may be reduced.

The rapid cooling device 300 may be configured as a housing including awindow 310 through which the generated terahertz wave may betransmitted. The inspection target object 130 may pass through theinside of the housing of the rapid cooling device 300. For example, thewindow 310 may be formed of a heat insulating foam which has a highinsulation effect and allows a terahertz wave to easily passtherethrough.

The defrosting device 320 may be disposed at a rear end of the rapidcooling device 300 and defrost the rapidly cooled inspection targetobject 130.

The structure of the rapid cooling device 300 in this embodiment ismerely an embodiment shown for the purpose of explanation, and the rapidcooling device 300 may be realized by various types of structures.

Since the inspection target object 130 is rapidly cooled for theterahertz wave to be easily transmitted therethrough, the highresolution inspection apparatus using a terahertz Bessel beam may alsoinspect the inspection target object containing moisture with highresolution.

FIG. 4 is a view illustrating a high resolution inspection apparatususing a Bessel beam according to another embodiment of the presentinvention.

Referring to FIG. 4, a high resolution inspection apparatus 400 using aBessel beam may include a terahertz wave optical head 410, an inspectiontarget object 420, and a terahertz wave concentrating head 430. Althoughnot illustrated in FIG. 4, the scanner 110, the first transfer unit 150,and the second transfer unit 160 illustrated in FIG. 1 may further beincluded in this embodiment.

The terahertz wave optical head 410 may include a terahertz wavegenerating unit 411, an angle changing unit 412, and a Bessel beamforming unit 413. In the present embodiment, a case where the terahertzwave generating unit 411, the angle changing unit 412, and the Besselbeam forming unit 413 are all included in the terahertz wave opticalhead 410 will be described as a reference, but the terahertz waveoptical head 410 may be realized by including only some of the terahertzwave generating unit 411, the angle changing unit 412, and the Besselbeam forming unit 413.

A Bessel beam is an electromagnetic wave given as a zero-th-order Besselfunction of the first kind in a solution set of Maxwell's equationsabout a free space and has been known as a non-diffractive beam. TheBessel beam was first introduced by Durnin in 1987 and has axialasymmetry, in which energy is concentrated as much as a predeterminedlength about an axis in the shape of a needle. Since it is implementedby an optical system having not an infinite aperture, but a limitedaperture, there is no Bessel beam that travels infinitely, so it is alsousually called a quasi-Bessel-beam (QBB). The QBB is made by a hologram,a combination of a lens and a circular mask composed of a plurality ofrings or limited apertures, or a conical lens known as an axicon.

The terahertz wave generating unit 110 may generate a terahertz wave.The terahertz wave refers to an electromagnetic wave in a terahertzregion and preferably has a frequency of 0.1 THz to 10 THz. However,although a terahertz wave is slightly outside the range, if the range iseasily conceivable by a person skilled in the art to which the presentinvention pertains, the terahertz wave may be regarded as the terahertzwave of the present invention.

The angle changing unit 120 may change an angle of the terahertz waveincident from the terahertz wave generating unit 411, to be smaller andto enter the Bessel beam forming unit 413. For example, the anglechanging unit 412 may change the incident terahertz wave to apredetermined angle or smaller or parallel with respect to the opticalaxis. The angle changing unit 412 may be a convex lens for refractingthe incident terahertz wave in parallel or a parabolic reflectorreflecting the incident terahertz wave in parallel.

The Bessel beam forming unit 413 may form a terahertz Bessel beam on atleast a portion of the inspection target object using the terahertz waveincident from the angle changing unit 412.

When the angle changing unit 412 is not provided, the Bessel beamforming unit 413 may form the terahertz Bessel beam on at least aportion of the inspection target object using the terahertz waveincident from the terahertz wave generating unit 411.

Since it is difficult for the Bessel beam forming unit 413 to form anideal Bessel beam in reality, the Bessel beam formed by the Bessel beamforming unit 413 may be called a quasi-Bessel beam (QBB). Aconfiguration of forming the Bessel beam by the Bessel beam forming unit413 will be described in more detail with reference to FIG. 2.

The Bessel beam forming unit 413 may be disposed such that a terahertzwave whose angle is changed by the angle changing unit 412 is incidenton be perpendicular with respect to a light incident surface of theBessel beam forming unit 413.

The Bessel beam forming unit 413 may be configured as various types.That is, the Bessel beam forming unit 413 may include a diffractiveoptical element including a plurality of circular recesses or circularholes and a lens having a positive refractive index, or may beconfigured as an axicon lens or a hologram optical element.

The Bessel beam forming unit 413 may be a first axicon lens at which adiameter of a terahertz Bessel beam focused on the inspection targetobject is smaller than a wavelength of the terahertz wave generated bythe terahertz wave generating unit. In this embodiment, the apical anglethat forms the diameter of the terahertz Bessel beam which is equal toor smaller than the wavelength is defined as a maximum apical angle.

In this case, a maximum value of the apical angle τ of the first axiconlens may be calculated through equations below using a diameter(ρ_(FWHM)) of a full width at half maximum, a wavelength (λ), and arefractive index (n, n₀).

$\begin{matrix}{{{J_{0}\left( {k\;\rho\;\sin\;\alpha_{0}} \right)}^{2} = {{J_{0}\left( {{1.1}264} \right)}^{2} = 0.5}}{\rho_{FWHM} = \frac{1.1264}{k\;\sin\;\alpha_{0}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, J0(z) is a zero-th-order Bessel function, and in order to satisfyJ₀ ²(z)=0.5, J₀(z) must be 1/√{square root over (²)} (J₀(z)=1/√{squareroot over (²)}). Here, z satisfying this value is 1.1264 (z=1.1264).Thus, Equation 1 may be derived from equation 1.1264=k*ρ_(FWHM)*sin α₀.In J₀ ²(z)=0.5, the value 0.5 may be changed.

$\begin{matrix}{{\alpha_{0} = {{\arcsin\left( {\frac{n}{n_{0}}{\cos\left( \frac{\tau}{2} \right)}} \right)} + \frac{\tau - \pi}{2}}},\left( {0 < \alpha_{0} < \frac{\tau}{2}} \right)} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \\{k = \frac{2\pi}{\lambda}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack \\{\rho_{FWHM} = \frac{1.1264}{\frac{2\pi}{\lambda}{\sin\left\lbrack {{\arcsin\left( {\frac{n}{n_{0}}{\cos\left( \frac{\tau}{2} \right)}} \right)} + \frac{\tau - \pi}{2}} \right\rbrack}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, J₀: zero-th-order Bessel function

ρ_(FWHM): full width at half maximum of focused terahertz Bessel beam

λ: wavelength of terahertz wave

α₀: half value of crossing angle of terahertz wave crossing afterpassing through axicon lens

n: refractive index of first axicon lens

n₀: average refractive index of surrounding environment

τ: apical angle of first axicon lens

[Equation 4] is an equation derived using [Equation 1], [Equation 2],and [Equation 3].

Meanwhile, a minimum value of the apical angle of the first axicon lensmay be an apical angle of the first axicon lens where total internalreflection according to the refractive index of the first axicon doesnot occur.

Thus, the apical angle of the first axicon lens at which the diameter ofthe terahertz Bessel beam is formed to be smaller than the wavelength ofthe terahertz wave generated by the terahertz wave generating unit maybe formed between the maximum value and the minimum value recognized asdescribed above.

The inspection target object 420 is a target object to be inspected andmay be disposed between the terahertz wave optical head 410 and theterahertz wave concentrating head 430.

The terahertz wave concentrating head 430 includes a first lens 431, asecond lens 432, and a detection unit 433. In this embodiment, the casewhere the first lens 431, the second lens 432, and the detection unit433 are included in the terahertz wave concentrating head 430 isdescribed as a reference, but the terahertz wave concentrating head 430may include only some of the first lens 431, the second lens 432, andthe detection unit 433.

The first lens 431 may change the angle of the terahertz wave radiatedwhen the terahertz Bessel beam generated by the Bessel beam forming unit413 is transmitted through the inspection target object 420. Forexample, the first lens 431 may change the angle of the terahertz wave,to be smaller than or equal to a predetermined angle with respect to theoptical axis.

The second lens 432 may concentrate the terahertz wave passing throughthe first lens 431 to the detection unit 433.

In the present invention, the high-resolution terahertz waveconcentrating module refers to a device including the first lens 431 andthe second lens 432. For example, the high-resolution terahertz wave isspread in the form of a ring-shaped circular beam away from the Besselbeam forming unit 413, and here, the high-resolution terahertz waveconcentrating module (first lens and second lens) concentrates thecircularly spreading terahertz wave so that concentrated terahertz wavemay travel toward the detection unit 433.

For example, the high-resolution terahertz wave concentrating module maybe realized in various types of components such as a convex lens, aconcave mirror, a parabolic reflector, an ellipsoidal mirror, and thelike.

The detection unit 433 may detect the terahertz wave concentrated by thesecond lens. For example, the detection unit 433 may detect an intensityof the terahertz wave. For example, the detection unit 433 may berealized to include a Schottky diode.

An image generating unit (not shown) may generate an image using theBessel beam detected through the detection unit 433. The generated imagemay be displayed on a display unit (not shown).

The high-resolution inspection apparatus using a Bessel beam mayconcentrate the terahertz wave transmitted through the inspection targetobject with little loss, thereby increasing concentration efficiency.

Further, in the high resolution inspection apparatus using the Besselbeam, the diameter of the terahertz wave reaching the detection unit isregulated to be equal to or less than the wavelength of the terahertzwave, whereby a clear image may be obtained by increasing resolution.

FIG. 5 is a view illustrating a Bessel beam forming unit according to anembodiment of the present invention.

Referring to FIG. 5, the Bessel beam forming unit may include an axicon500. R is a radius of the axicon lens, τ is an apical angle of theaxicon lens, α₀ is half of a crossing angle of a beam crossing afterpassing through the axicon lens, and w₀ is a radius of parallel lightincident on the axicon lens. In addition, a section in which the Besselbeam is formed is denoted by Z_(max) in FIG. 5, and the terrahertz waveincident on the axicon lens is subjected to constructive interference inthis section and energy gathers toward the center along the z axis.

Here, a Gaussian beam incident on the axicon lens and the Bessel beamformed by the axicon lens are distributed to have axial symmetry, and afield is distributed in a circular shape along the z axis. That is, whenviewed in a direction from the left to the right in FIG. 5, both theGaussian beam in front of the axicon lens and the Bessel beam in therear of the axicon lens are formed to have a circular shape. Inparticular, the Bessel beam formed by the axicon lens spreads as aring-shaped circular beam away from the axicon lens.

Meanwhile, in a transmission image obtained from each point being drawnat a time as with raster scanning, the most important factor determiningresolution of the image is a diameter of a beam incident on aninspection target object 1.

In particular, in the case of the Bessel beam formed by an axicon lens,a diameter thereof is determined by the wavelength of terahertz wave andα₀, and here, α₀ may be obtained using Equation 1 according to theSnell's law.

$\begin{matrix}{{\alpha_{0} = {{\arcsin\left( {\frac{n}{n_{0}}{\cos\left( \frac{\tau}{2} \right)}} \right)} + \frac{\tau - \pi}{2}}},\left( {0 < \alpha_{0} < \frac{\tau}{2}} \right)} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Here, n₀ denotes a refractive index in the air, n denotes a refractiveindex of the axicon lens, and τ denotes an apical angle of the axiconlens.

Meanwhile, Z_(max) corresponds to a depth of focus, and the depth offocus may be expressed by Equation 6 below.Z _(max) =w ₀/tan α₀  [Equation 6]

Here, w₀ denotes a radius of the beam incident on the axicon lens asillustrated in FIG. 5. Referring to this equation, it can be seen thatthe depth of focus also relies on α₀.

Accordingly, from these viewpoints, it can be seen that the resolutionand the depth of focus of the image are significantly changed mainly bythe value α₀.

Based on this, α₀ and the depth of focus may be calculated on theassumption that n₀ is 1.0, n is 1.54 (high density polyethylene), τ is150°, and R is 25 mm regarding the axicon lens illustrated in FIG. 5.

First, when α₀ is calculated using Equation 5, α₀ may be calculated to8.5°. Further, when the depth of focus (Z_(max)) is calculated usingEquation 6, Z_(max) may be calculated to 40.2 mm.

The Bessel beam forming unit may include a diffractive optical elementin which a plurality of circular recesses or circular holes are arrangedconcentrically and a lens having a positive refractive index. Here, thecircular recesses or holes formed in the diffractive optical element maybe formed to be concavely recessed or penetrating through thediffractive optical element. The lens having such a positive refractiveindex is disposed on the opposite side of a direction in which parallellight is incident with respect to the diffractive optical element.

In addition to the present embodiment, the Bessel beam forming unit maybe configured in various forms such as a hologram structure, or thelike.

FIG. 6 is a view illustrating calculation of a diameter of a terahertzwave beam focused on different apical angles using Equation 4.

Referring to FIG. 6, it can be seen that, when the wavelength λ of theterahertz wave is 2.14 mm, the refractive index n of the first axiconlens is 1.54, and the average refractive index n₀ of the surroundingenvironment is 1, a maximum value of the apical angle τ of the firstaxicon lens is about 119 and a minimum value of the apical angle τ ofthe first axicon lens is about 99.

FIGS. 7 and 8 are views illustrating an inspection apparatus forconcentrating light using a single lens.

Referring to FIGS. 7 and 8, an inspection apparatus 700 includes aterahertz wave generating unit 710, an angle changing unit 720, a Besselbeam forming unit 730, a light concentrating unit 740, and a detectionunit 750.

The terahertz wave generating unit 710 may generate a terahertz wave.

The angle changing unit 720 may change the angle of the terahertz waveincident from the terahertz wave generating unit 710, to be smaller andto enter the Bessel beam forming unit 730.

The Bessel beam forming unit 730 may form a terahertz Bessel beam on atleast a portion of the inspection target object using the terahertz waveincident from the angle changing unit 720. For example, the Bessel beamforming unit may be an axicon. The inspection target object may beformed between the Bessel beam forming unit 730 and the lightconcentrating unit 740.

The light concentrating unit 740 may be implemented as a single lens.

The detection unit 750 may detect the terahertz wave concentrated by thelight concentrating unit 740.

Referring to FIG. 7, when the apical angle of the axicon, which is theBessel beam forming unit 730, is 140°, a radius of the terahertz wavetransmitted through the inspection target object and incident on thedetection unit 750 is about 5.1 mm, and thus, a diameter of theterahertz wave at the detection unit 750 is about 10.2 mm.

In this case, most of the terahertz waves incident from the lightconcentrating unit 740 using a single lens have a diameter of about 9 mmand may be concentrated on the detection unit 750 having a horn.

Referring to FIG. 8, in order to form the diameter of the terahertzBessel beam focused on the inspection target object, to be equal to orsmaller than the wavelength of the terahertz wave, the apical angle ofthe axicon must be small. In other words, the apical angle of the axiconmust be small to realize high resolution. Thus, the angle was formed tobe 110° smaller than the apical angle of the axicon in FIG. 7.

When the apical angle of the axicon, which is the Bessel beam formingunit 730, is 110°, the radius of the terahertz wave incident on thedetection unit 750 after being transmitted through the inspection targetobject is about 17 mm, and thus, the diameter of the terahertz wave atthe inspection unit 750 is about 34 mm.

As the diameter of the terahertz wave incident on the detector 750increases, only a portion of the terahertz waves incident from the lightconcentrating unit 740 using a single lens is concentrated on thedetection unit 750. In other words, a large amount of the terahertzwaves incident from the light concentrating unit 740 is not incident onthe detection unit 750, significantly degrading detection performance ofthe detection unit 750 is remarkably deteriorated.

FIG. 9 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 4 according to a first embodiment.

Referring to FIG. 9, the high resolution inspection apparatus 900includes a terahertz wave generating unit 910, an angle changing unit920, a Bessel beam forming unit 930, a first lens 940, a second lens750, and a detection unit 960.

The terahertz wave generating unit 910 may generate a terahertz wave.

The angle changing unit 920 may change the angle of the terahertz waveincident from the terahertz wave generating unit 910 to be smaller andto enter the Bessel beam forming unit 930.

The Bessel beam forming unit 930 may form a terahertz Bessel beam on atleast a portion of the inspection target object using the terahertz waveincident from the angle changing unit 920. For example, the Bessel beamforming unit may be an axicon.

The inspection target object may be formed between the Bessel beamforming unit 930 and the first lens 940.

The Bessel beam forming unit 930 may be a first axicon lens having anapical angle at which the diameter of the terahertz Bessel beam isformed to be smaller than the wavelength of the terahertz wave generatedby the terahertz wave generating unit.

A maximum value of the apical angle of the first axicon lens may becalculated on the basis of Equation 1 to Equation 3. For example, whenthe wavelength λ of the terahertz wave is 2.14 mm, a refractive index nof the first axicon lens is 1.54, and an average refractive index n₀ ofthe surrounding environment is 1, the apical angle τ of the first axiconlens has a value of about 119°. Thus, a maximum value of the apicalangle of the first axicon lens is about 119°.

Meanwhile, a minimum value of the first axicon lens may be an apicalangle of the first axicon lens at which total internal reflectionaccording to the refractive index of the first axicon does not occur.Regarding the refractive index in this embodiment, a critical angle dueto total internal reflection is 99°. Therefore, the minimum value of theapical angle of the first axicon lens is about 99°.

Ultimately, the diameter of the terahertz Bessel beam is formed to besmaller than the wavelength of the terahertz wave generated by theterahertz wave generating unit only when the apical angle of the firstaxicon lens falls between the maximum value 119° to the minimum value99°.

The first lens 940 may change the angle of the terahertz wave radiatedwhen the terahertz Bessel beam generated by the Bessel beam forming unit930 is transmitted through the inspection target object.

The first lens 940 may be a second axicon lens arranged to besymmetrical to the first axicon lens 930 with respect to the inspectiontarget object.

The second axicon lens 950 may have an apical angle equal to that of thefirst axicon lens 930. In this case, the size of the second axicon lens950 may be smaller than or equal to the size of the first axicon lens930. When the apical angle of the second axicon lens is equal to that ofthe first axicon lens 930, efficiency of concentrating the terahertzwave on the detection unit 950 is the highest.

If the angle changing unit 920 is a first convex lens, the second lens950 may be a second convex lens arranged to be symmetrical to the firstconvex lens with respect to the inspection target object.

When the wavelength λ of the terahertz wave is 2.14 mm and the firstaxicon lens of the Bessel beam forming unit 930 has an angle of 110°,the radius of the terahertz wave in the detection unit 960 is 0.006 mm,and thus, the diameter of the terahertz wave is 0.012 mm.

Since the terahertz wave is concentrated using the first lens 940 andthe second lens 950, the diameter of the terahertz wave concentrated onthe detection unit 960 may be significantly smaller than the diameter ofthe terahertz wave concentrated on the detection unit 950 of FIG. 8,thus increasing concentration efficiency.

Therefore, when the terahertz wave is concentrated using the first lens940 and the second lens 950, although the apical angle of the firstaxicon lens is small, resolution may be significantly increased withhigh concentration efficiency, and thus, high resolution inspectionimage may be obtained.

FIG. 10 is a view illustrating the high-resolution inspection apparatusof FIG. 4 according to a second embodiment.

Referring to FIG. 10, the high resolution inspection apparatus 1000includes a terahertz wave generating unit 1010, an angle changing unit1020, a Bessel beam forming unit 1030, an inspection target object 1040,a first lens 1050, a second lens 1060, and a detection unit 1070.

The terahertz wave generating unit 1010 may generate a terahertz wave.

The angle changing unit 1020 may change the angle of the terahertz waveincident from the terahertz wave generating unit 1010, to be smaller andto enter the Bessel beam forming unit 1030.

The Bessel beam forming unit 1030 may form a terahertz Bessel beam on atleast a portion of the inspection target object using the terahertz waveincident from the angle changing unit 1020. For example, the Bessel beamforming unit may be an axicon.

The inspection target object may be formed between the Bessel beamforming unit 1030 and the light concentrating unit 1040.

The Bessel beam forming unit 1030 may be a first axicon lens having anapical angle at which the diameter of the terahertz Bessel beam issmaller than the wavelength of the terahertz wave generated by theterahertz wave generating unit.

The first lens 1040 may be a third convex lens changing the angle of theterahertz wave radiated when the terahertz Bessel beam passes throughthe inspection target object, to be smaller.

The second lens 1050 may be a fourth convex lens arranged to besymmetrical to the third convex lens with respect to the axisperpendicular to the optical axis.

When the wavelength λ of the terahertz wave is 2.14 mm, the radius ofthe terahertz wave incident on the detection unit 1060 after beingtransmitted through the inspection target object is about 2.5 mm, andthus, the diameter of the terahertz wave at the detection unit is about5 mm.

Since the terahertz wave is concentrated using the first lens 1040 andthe second lens 1050, the diameter of the terahertz wave issignificantly smaller than the diameter of the terahertz waveconcentrated to the detection unit 750 of FIG. 8, and thus, condensationefficiency may be enhanced. Thus, the high resolution inspectionapparatus according to the present embodiment may significantly increaseresolution with high concentration efficiency even when the apical angleof the first axicon lens is small, thus obtaining a high resolutioninspection image.

FIG. 11 is a view illustrating the high-resolution inspection apparatusof FIG. 4 according to a third embodiment.

Referring to FIG. 11, a high resolution inspection apparatus 1100includes a terahertz wave generating unit 1110, an angle changing unit1120, a Bessel beam forming unit 1130, an inspection target object 1140,a first lens 1150, a second lens 1160, and a detection unit 1170.

The terahertz wave generating unit 1110 may generate a terahertz wave.

The angle changing unit 1120 may change the angle of the terahertz waveincident from the terahertz wave generating unit 1110, to be smaller andto enter the Bessel beam forming unit 1130.

The Bessel beam forming unit 1130 may form a terahertz Bessel beam on atleast a portion of the inspection target object using the terahertz waveincident from the angle changing unit 1120. For example, the Bessel beamforming unit may be an axicon.

The inspection target object may be formed between the Bessel beamforming unit 1130 and the light concentrating unit 1140.

The Bessel beam forming unit 1130 may be a first axicon lens having anapical angle at which the diameter of the terahertz Bessel beam issmaller than the wavelength of the terahertz wave generated by theterahertz wave generating unit.

The first lens 1140 may be a second axicon lens arranged to besymmetrical to the first axicon lens 1130 with respect to the inspectiontarget object.

The second axicon lens may have an apical angle having the same size asthat of the first axicon lens 1130.

The second lens 1150 may have the same shape as the second axicon lens1140 and may be arranged to be symmetrical to the second axicon lens1140 with respect to the axis perpendicular to the optical axes.

When the wavelength λ of the terahertz wave is 2.14 mm, the radius ofthe terahertz wave transmitted through the inspection target object soas to be incident on the detection unit 1160 is about 1.7 mm, and thus,the diameter of the terahertz wave at the detection unit 1160 is about3.4 mm.

Since the terahertz wave is concentrated using the first lens 1140 andthe second lens 1150, the diameter of the terahertz wave may besignificantly smaller than the diameter of the terahertz waveconcentrated on the detection unit 750 of FIG. 8, thus increasingconcentration efficiency. Thus, the high resolution inspection apparatusaccording to the present embodiment may increase resolution with highconcentration efficiency even when the apical angle of the first axiconlens is small, thus obtaining a high resolution inspection image.

FIGS. 12 and 13 are transmission images obtained by measuring aninspection target object using the apparatuses of FIGS. 8 to 11.

Specifically, FIG. 12 shows an inspection target object measured usingthe apparatus illustrated in FIG. 8, and FIG. 13 shows an inspectiontarget object measured using the apparatus illustrated in FIGS. 8 to 11.

Referring to FIG. 12, it can be seen that the inspection target objectcannot be identified at all with the transmission image obtained byconcentrating light with only a single lens.

In contrast, referring to FIG. 13, it can be seen that the inspectiontarget object can be clearly identified with the transmission imageobtained by concentrating light with the lens configuration illustratedin FIGS. 8 to 11.

As described above, the high resolution image may be obtained using thehigh resolution inspection apparatus using a Bessel beam according tothe present invention.

FIG. 14 is a view illustrating a high resolution inspection apparatususing a terahertz Bessel beam according to another embodiment of thepresent invention.

Referring to FIG. 14, a high resolution inspection apparatus 1400 usinga Bessel beam may include a terahertz wave optical head 1410, aninspection target object 1420, and a terahertz wave concentrating head1430. Although not illustrated in FIG. 14, the scanner 110, the firsttransfer unit 150, and the second transfer unit 160 illustrated in FIG.1 may be additionally provided in this embodiment.

The terahertz wave optical head 1410 may include a terahertz wavegenerating unit 1411, an angle changing unit 1412, a Bessel beam formingunit 1413, and a ring beam forming unit 1414. In the present embodiment,a case where all the angle changing unit 1412, the Bessel beam formingunit 1413, and the ring beam forming unit 1414 are all included in theterahertz wave optical head 1410 will be described as a reference, butthe terahertz wave optical head 1410 may be realized to include onlysome of the angle changing unit 1412, the Bessel beam forming unit 1413,and the ring beam forming unit 1414.

The terahertz wave generating unit 1411 may generate a terahertz wave.

The angle changing unit 1412 may change the angle of the terahertz waveincident from the terahertz wave generating unit 1411 to be smaller andto enter the Bessel beam forming unit 1413. For example, the anglechanging unit 1412 may change the incident terahertz wave to an angleequal to or smaller than a predetermined angle with respect to theoptical axis, or to form the incident terahertz wave in parallel. Theangle changing unit 1412 may be a convex lens refracting the incidentterahertz wave in parallel or a parabolic reflector reflecting theincident terahertz wave in parallel.

The Bessel beam forming unit 1413 may generate a terahertz Bessel beamusing the terahertz wave incident from the angle changing unit 1412.

When the angle changing unit 1412 is not provided, the Bessel beamforming unit 1413 may form a terahertz Bessel beam using the terahertzwave incident from the terahertz wave generating unit 1411.

Since it is difficult for the Bessel beam forming unit 1413 to form anideal Bessel beam in reality, the Bessel beam formed by the Bessel beamforming unit 1413 may be called a quasi-Bessel beam (QBB). Aconfiguration of forming the Bessel beam by the Bessel beam forming unit1413 has already been described above with reference to FIG. 5.

The Bessel beam forming unit 1413 may be disposed such that a terahertzwave whose angle is changed by the angle changing unit 1412 is incidenton be perpendicular with respect to a light incident surface of theBessel beam forming unit 1413.

The Bessel beam forming unit 1413 may be a fourth axicon lens at which adiameter of a terahertz Bessel beam focused on the inspection targetobject is smaller than the wavelength of the terahertz wave generated bythe terahertz wave generating unit. In this embodiment, the apical anglethat forms the diameter of the terahertz Bessel beam which is equal toor smaller than the wavelength is defined as a maximum apical angle.

In this case, a maximum value of the apical angle τ of the fourth axiconlens may be calculated through equations below using a diameter(ρ_(FWHM)) of a full width at half maximum, a wavelength (λ), and arefractive index (n, n₀). Details thereof have already been describedabove with reference to FIG. 4, and thus, a redundant description willbe omitted.

The ring beam forming unit 1414 may form a ring beam using the terahertzBessel beam and concentrate the formed ring beam to the inspectiontarget object 1420.

For example, the ring beam forming unit 1420 may concentrate theterahertz Bessel beam radiated after having been focused through theBessel beam forming unit 1413 on the inspection target object again inthe form of a ring-shaped circular beam.

For example, the ring beam forming unit 1420 may be a third lens forminga ring beam and concentrates the formed ring beam on the inspectiontarget object.

The ring beam forming unit 1420 will be described in detail withreference to FIGS. 15 to 23.

The inspection target object 1420 refers to a target object to beinspected and may be disposed between the terahertz wave optical head1410 and the terahertz wave concentrating head 1430.

The terahertz wave concentrating head 1430 may include a ring beamdetecting unit 1431 and a scattered light detecting unit 1432. Althoughnot illustrated in this embodiment, the first lens and the second lens(the ‘light concentrating unit’) described above with respect to FIGS. 4to 11 may further be included between the inspection target object 1420and the terahertz wave concentrating head 1430. Thus, since the firstlens and the second lens concentrate the ring beam transmitted throughthe inspection target object 1420 on the ring beam detecting unit 1431,resolution of the inspection apparatus may be enhanced.

The ring beam detecting unit 1431 may detect the ring beam transmittedthrough the inspection target object 1420.

The scattered light detecting unit 1432 may detect scattered lightgenerated from the inspection target object 1420. For example, thescattered light detecting unit 1432 may include a reflected scatteredlight detecting unit capable of detecting scattered light reflected fromthe object 1420 or a transmitted scattered light detecting unit capableof detecting scattered light transmitted from the object 1420.

The image generating unit (not shown) may generate an image using theBessel beam detected through the ring beam detecting unit 1431 and thescattered light detecting unit 1432. The generated image may bedisplayed on a display unit (not shown).

A high resolution inspection apparatus using a Bessel beam may form aring beam without loss of the terahertz wave, thereby enhancing thecontrast of a transparent inspection target object.

Further, the high resolution inspection apparatus using a Bessel beammay increase the contrast of the transparent inspection target object bydetecting scattered light generated from the inspection target object.

Further, in the high resolution inspection apparatus using a Besselbeam, since the scattered light detecting unit is disposed inside thegenerated ring beam, a separate space due to an addition of thescattered light detecting unit is not necessary, thus obtainingminiaturization.

In the high resolution inspection apparatus using a Bessel beam,although the apical angle of the axicon of the Bessel beam forming unitis regulated to be small to obtain high resolution, a high resolutionimage may be obtained by reducing the diameter of the ring beamgenerated using two lenses of the ring beam forming unit.

FIG. 15 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a firstembodiment.

Referring to FIG. 15, a high resolution inspection apparatus 1500 usinga Bessel beam includes a terahertz wave generating unit 1510, an anglechanging unit 1520, a Bessel beam forming unit 1530, a ring beam formingunit 1540, an inspection target object 1550, a ring beam detecting unit1560, a transmitted scattered light detecting unit 1570, and a reflectedscattered light detecting unit 1571.

The terahertz wave generating unit 1510 may generate a terahertz wave.

The angle changing unit 1520 may change the angle of the terahertz waveincident from the terahertz wave generating unit 1510 to be smaller andto enter the Bessel beam forming unit 1530.

The Bessel beam forming unit 1530 may form a terahertz Bessel beam usingthe terahertz wave incident from the angle changing unit 1520. Forexample, the Bessel beam forming unit may be an axicon.

The ring beam forming unit 1540 may be a third lens forming a ring beamusing the terahertz Bessel beam incident from the Bessel beam formingunit 1530 and concentrating the formed ring beam on the inspectiontarget object 1550.

The ring beam detecting unit 1560 may detect a ring beam transmittedthrough the inspection target object 1550.

The transmitted scattered light detecting unit 1570 may detect scatteredlight transmitted from the inspection target object 1550. For example,the transmitted scattered light detecting unit 1570 may be disposedinside the ring beam incident from the third lens. In this manner, sincethe transmitted scattered light detecting unit 1570 is disposed insidethe ring beam, an overall size of the apparatus is not changed althoughthe transmitted scattered light detecting unit 1570 is additionallyprovided.

The reflected scattered light detecting unit 1571 may be disposed insidethe ring beam exiting from the third lens 1540, which is a ring beamforming unit, and may be provided in the third lens 1540.

FIG. 16 is a view illustrating the ring beam forming unit 1540 of FIG.15.

Referring to FIG. 16, the ring beam forming unit 1540 may include amember capable of accommodating the reflected scattered light detectingunit 1571. For example, the ring beam forming unit 1540 may include ahole 1600, and the reflected scattered light detecting unit 1571 may bedisposed inside the hole 1600. For example, the reflected scatteredlight detecting unit 1571 may be disposed inside the ring beam formingunit 1540 and may be disposed inside the ring beam exiting from thethird lens 1540. In this manner, since the reflected scattered lightdetecting unit 1571 is disposed inside the ring beam forming unit 1540,an overall size of the apparatus is not changed although the reflectedscattered light detecting unit 1571 is additionally provided.

The high resolution inspection apparatus using a Bessel beam mayincrease the contrast of a transparent inspection target object bydetecting scattered light generated from the inspection target object.

Further, in the high-resolution inspection apparatus using a Besselbeam, since the scattered light detecting unit is disposed inside thegenerated ring beam, a separate space due to an addition of thescattered light detecting unit is unnecessary, thus obtainingminiaturization.

FIG. 17 is a view illustrating the high resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a secondembodiment.

Referring to FIG. 17, a high resolution inspection apparatus 1700 usinga Bessel beam includes a terahertz wave generating unit 1710, an anglechanging unit 1720, a Bessel beam forming unit 1730, a ring beam formingunit 1740, an inspection target object 1750, a ring beam detecting unit1760, a path changing unit 1770, a transmitted scattered light detectingunit 1780, and a reflected scattered light detecting unit 1781.

The terahertz wave generating unit 1710, the angle changing unit 1720,the Bessel beam forming unit 1730, the ring beam forming unit 1740, andthe inspection target object 1750 have already been described, and thus,a redundant description will be omitted.

The ring beam detecting unit 1760 may detect a ring beam transmittedthrough the inspection target object 1750.

The path changing unit 1770 may change a path of scattered lightreflected from the inspection target object 1750. For example, the pathchanging unit 1770 may cause the reflected scattered light from theinspection target object 1750 to be incident on the reflected scatteredlight detecting section 1781.

The path changing unit 1770 may be various types of devices capable ofmaking the scattered light incident on the reflected scattered lightdetecting unit 1781.

The ring beam forming unit 1740 may include a member capable ofaccommodating the path changing unit 1770.

The transmitted scattered light detecting unit 1780 may detect scatteredlight transmitted from the inspection target object 1750. For example,the transmitted scattered light detecting unit 1780 may be disposedinside the ring beam incident from the third lens. In this manner, sincethe transmitted scattered light detecting unit 1780 is disposed insidethe ring beam, an overall size of the apparatus is not changed althoughthe transmitted scattered light detecting unit 1780 is additionallyprovided.

The reflected scattered light detecting unit 1781 may detect scatteredlight incident from the path changing unit 1770.

The high resolution inspection apparatus using a Bessel beam mayincrease the contrast of a transparent inspection target object bydetecting scattered light generated from the inspection target object.

FIG. 18 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a thirdembodiment.

Referring to FIG. 18, a high resolution inspection apparatus 1800 usinga Bessel beam includes a terahertz wave generating unit 1810, an anglechanging unit 1820, a Bessel beam forming unit 1830, ring beam formingunits 1840 and 1850, an inspection target object 1860, a ring beamdetecting unit 1870, a transmitted scattered light detecting unit 1880,and a reflected scattered light detecting unit 1881.

The terahertz wave generating unit 1810, the angle changing unit 1820,the Bessel beam forming unit 1830, the inspection target object 1860,the ring beam detecting unit 1870, the transmitted scattered lightdetecting unit 1880, and the reflected scattered light detecting unit1881 have already been described above with reference to FIG. 17, andthus, a redundant description will be omitted.

The ring beam forming units 1840 and 1850 may include a fourth lens 1840changing the angle of the terahertz Bessel beam incident from the Besselbeam forming unit to be smaller and to enter the third lens 1850 and thethird lens 1850 forming a ring beam using the terahertz Bessel beamincident from the fourth lens 1840 and concentrating the formed ringbeam on the inspection target object 1860.

In a case where the Bessel beam forming unit 1830 is a fourth axiconlens, the fourth lens 1840 may be a fifth axicon lens arranged to besymmetrical to the fourth axicon lens 1830 with respect to a lineperpendicular to the optical axis.

The fifth axicon lens 1840 may have an apical angle having the same sizeas that of the fourth axicon lens 1830. In this case, the size of thefifth axicon lens may be smaller than, equal to, or greater than thesize of the fourth axicon lens 1830.

The third lens 1850 may be a sixth axicon lens having the same shape asthe fifth axicon lens 1840 and arranged to be symmetrical to the fifthaxicon lens 1840 with respect to the axis perpendicular to the opticalaxis.

In this manner, since the ring beam forming unit is realized using thefourth lens 1840 and the third lens 1850, although the apical angle ofthe fourth axicon lens is reduced to improve resolution, the diameter ofthe ring beam incident on the inspection target object may be reduced.

Therefore, resolution may be significantly increased, thus obtaininghigh-resolution reflection and transmission inspection images.

FIG. 19 is a view illustrating the high-resolution inspection apparatususing the terahertz Bessel beam of FIG. 14 according to a fourthembodiment.

Referring to FIG. 19, a high resolution inspection apparatus 1900 usinga Bessel beam includes a terahertz wave generating unit 1910, an anglechanging unit 1920, a Bessel beam forming unit 1930, ring beam formingunits 1940 and 1950, an inspection target object 1960, a ring beamdetecting unit 1970, a transmitted scattered light detecting unit 1980,and a reflected scattered light detecting unit 1981.

The terahertz wave generating unit 1910, the angle changing unit 1920,the Bessel beam forming unit 1930, the inspection target object 1960,the ring beam detecting unit 1970, the transmitted scattered lightdetecting unit 1980, and the reflected scattered light detecting unit1981 have already been described above with reference to FIG. 17, andthus, a redundant description will be omitted.

The angle changing unit 1920 may be a fifth convex lens changing theangle of the terahertz wave incident from the terahertz generating unit1910 to be smaller.

The ring beam forming units 1940 and 1950 may include a fourth lens 1940changing the angle of the terahertz Bessel beam incident from the Besselbeam forming unit to be smaller and to enter the third lens, and thethird lens 1950 forming a ring beam using the terahertz Bessel beamincident from the fourth lens 1940 and concentrating the formed ringbeam on the inspection target object 1960.

The fourth lens 1940 may be a seventh convex lens changing the angle ofthe terahertz wave that radiated when the terahertz Bessel beam istransmitted through the inspection target object.

The third lens 1950 may be an eighth convex lens disposed to besymmetrical to the fifth convex lens, which is the angle changing unit1920, with respect to the axis perpendicular to the optical axis and toface the seventh convex lens which is the fourth lens 1940. The seventhconvex lens and the eighth convex lens may have the same shape/size.

In this manner, since the ring beam forming unit is realized using thesecond lens and the first lens, although the apical angle of the fourthaxicon lens is reduced to increase resolution, the diameter of the ringbeam incident on the inspection target object may be reduced to besmall. Therefore, resolution may be significantly increased, thusobtaining high-resolution reflection and transmission inspection images.

FIG. 20 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a fifthembodiment.

Referring to FIG. 20, a high resolution inspection apparatus 2000 usinga Bessel beam includes a terahertz wave generating unit 2010, an anglechanging unit 2020, a Bessel beam forming unit 2030, ring beam formingunits 2040 and 2050, an inspection target object 2060, a ring beamdetecting unit 2070, a transmitted scattered light detecting unit 2080,and a reflected scattered light detecting unit 2081.

The terahertz wave generating unit 2010, the angle changing unit 2020,the Bessel beam forming unit 2030, the inspection target object 2060,the ring beam detecting unit 2070, the transmitted scattered lightdetecting unit 2080, and the reflected scattered light detecting unit2801 have already been described above with reference to FIG. 17, andthus, a redundant description will be omitted.

The angle changing unit 2020 may be a fifth convex lens changing theangle of the terahertz wave incident from the terahertz generating unit2010 to be smaller.

The ring beam forming units 2040 and 2050 may include a fourth lens 2040changing the angle of the terahertz Bessel beam incident from the Besselbeam forming unit to be smaller and to enter the third lens 2050, andthe third lens 2050 forming a ring beam using the terahertz Bessel beamincident from the fourth lens 2040 and concentrating the formed ringbeam on the inspection target object 2060.

In a case where the Bessel beam forming unit 2030 is a fourth axiconlens, the fourth lens 2040 may be a fifth axicon lens arranged to besymmetrical to the fourth axicon lens 2030 with respect to a lineperpendicular to the optical axis.

The third lens 2050 may be a sixth convex lens arranged to besymmetrical to the fourth convex lens, which is the angle changing unit2020, with respect to an axis perpendicular to the optical axis.

In this manner, since the ring beam forming unit is realized using thesecond lens and the first lens, although the apical angle of the fourthaxicon lens is reduced to increase resolution, the diameter of the ringbeam incident on the inspection target object may be reduced to besmaller. Therefore, resolution may be significantly increased, thusobtaining high-resolution reflection and transmission inspection images.

FIG. 21 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a sixthembodiment.

Referring to FIG. 21, a high resolution inspection apparatus 2100 usinga Bessel beam includes a terahertz wave generating unit 2110, an anglechanging unit 2120, a Bessel beam forming unit 2130, ring beam formingunits 2140 and 2150, an inspection target object 2160, a ring beamdetecting unit 2170, a path changing unit 2180, a transmitted scatteredlight detecting unit 2190, and a reflected scattered light detectingunit 2191.

The terahertz wave generating unit 2110, the angle changing unit 2120,the Bessel beam forming unit 2130, the inspection target object 2160,the ring beam detecting unit 2170, the path changing unit 2180, thetransmitted scattered light detecting unit 2190, and the reflectedscattered light detecting unit 2191 have already been described abovewith reference to FIG. 17, and thus, a redundant description will beomitted.

The ring beam forming units 2140 and 2150 may include a second lens 2140changing the angle of the terahertz Bessel beam incident from the Besselbeam forming unit to be smaller and to enter the third lens 2150, andthe third lens 2150 forming a ring beam using the terahertz Bessel beamincident from the fourth lens 2140 and concentrating the formed ringbeam on the inspection target object 2160.

In a case where the Bessel beam forming unit 2130 is a fourth axiconlens, the fourth lens 2140 may be a fifth axicon lens arranged to besymmetrical to the fourth axicon lens 2130 with respect to the lineperpendicular to the optical axis.

The fifth axicon lens 2140 may have an apical angle having the same sizeas that of the fourth axicon lens 2130.

In this case, the size of the fifth axicon lens may be smaller than,equal to, or larger than the size of the fourth axicon lens 2130. Whenthe apical angle of the fifth axicon lens is equal to that of the fourthaxicon lens 2130, efficiency of concentration of the terahertz wave onthe detection unit 2170 is the highest.

The third lens 2150 may be a fifth axicon lens having the same shape asthe fifth axicon lens 2140 and arranged to be symmetrical to the fifthaxicon lens 2140 with respect to the axis perpendicular to the opticalaxis.

FIG. 22 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to a seventhembodiment.

Referring to FIG. 22, a high resolution inspection apparatus 2200 usinga Bessel beam includes a terahertz wave generating unit 2210, an anglechanging unit 2220, a Bessel beam forming unit 2230, ring beam formingunits 2240 and 2250, an inspection target object 2260, a ring beamdetecting unit 2270, a path changing unit 2280, a transmitted scatteredlight detecting unit 2290 and a reflected scattered light detecting unit2291.

The terahertz wave generating unit 2210, the angle changing unit 2220,the Bessel beam forming unit 2230, the inspection target object 2260,the ring beam detecting unit 2270, the path changing unit 2280, thetransmitted scattered light detecting unit 2290, and the reflectedscattered light detecting unit 2291 have already been described abovewith reference to FIG. 17, and thus, a redundant description will beomitted.

The angle changing unit 2220 may be a fifth convex lens changing theangle of the terahertz wave incident from the terahertz generating unit2210 to be smaller.

The ring beams forming units 2240 and 2250 may include a fourth lens2240 changing the angle of the terahertz Bessel beam incident from theBessel beam forming unit to be smaller and to enter the third lens 2250,and the third lens 2250 forming a ring beam using the terahertz Besselbeam incident from the fourth lens 2240 and concentrating the formedring beam on the inspection target object 2260.

The third lens 2240 may be a seventh convex lens changing the angle ofthe terahertz wave radiated when the terahertz Bessel beam istransmitted through the inspection target object, to be smaller.

The third lens 2250 may be an eighth convex lens arranged to besymmetrical to the fifth convex lens, which is the angle changing unit2220, with respect to the axis perpendicular to the optical axis and toface the seventh convex lens which is the fourth lens 2240.

FIG. 23 is a view illustrating the high-resolution inspection apparatususing a terahertz Bessel beam of FIG. 14 according to an eighthembodiment.

Referring to FIG. 23, a high resolution inspection apparatus 2300 usinga Bessel beam includes a terahertz wave generating unit 2310, an anglechanging unit 2320, a Bessel beam forming unit 2330, ring beam formingunits 2340 and 2350, an inspection target object 2360, a ring beamdetecting unit 2370, a path changing unit 2380, a transmitted scatteredlight detecting unit 2390, and a reflected scattered light detectingunit 2391.

The terahertz wave generating unit 2310, the angle changing unit 2320,the Bessel beam forming unit 2330, the ring beam forming units 2340 and2350, the inspection target object 2360, the ring beam detecting unit2370, the path changing unit 2380, the transmitted scattered lightdetecting unit 2390, and the reflected scattered light detecting unit2391 have already been described above with reference to FIG. 17, andthus, a redundant description will be omitted.

The angle changing unit 2320 may be a fourth convex lens changing theangle of the terahertz wave incident from the terahertz generating unit2310 to be smaller.

The ring beams forming units 2340 and 2350 may include a fourth lens2340 changing the angle of the terahertz Bessel beam incident from theBessel beam forming unit to be smaller and to enter the third lens 2350,and the third lens 2350 forming a ring beam using the terahertz Besselbeam incident from the fourth lens 2340 and concentrating the formedring beam on the inspection target object 2360

In a case where the Bessel beam forming unit 2330 is a fourth axiconlens, the fourth lens 2340 may be a fifth axicon lens arranged to besymmetrical to the fourth axicon lens 2330 with respect to the lineperpendicular to the optical axis.

The third lens 2350 may be a sixth convex lens arranged to besymmetrical to the fifth convex lens, which is the angle changing unit2320, with respect to the axis perpendicular to the optical axis.

All of some of the embodiments may be selectively combined to beconfigured into various modifications.

Also, it should be appreciated that the embodiment is for descriptionand is not intended for limitation. Also, it will be understood by thoseskilled in the art that various changes and modifications may be madewithout departing from the spirit and scope of the invention.

The invention claimed is:
 1. A scattered light detection modulecomprising: a ring beam forming unit for forming a ring beam using aterahertz Bessel beam and concentrating the formed ring beam to aninspection target object and includes a first lens forming the ring beamand concentrating the formed ring beam to the inspection target objectwherein the first lens includes a member capable of accommodating areflected scattered light detecting unit; and the reflected scatteredlight detecting unit for detecting scattered light generated from theinspection target object and being disposed inside the member of thefirst lens.
 2. The reflected scattered light detection module of claim1, wherein the reflected scattered light detecting unit includes areflected scattered light detecting unit provided inside the ring beamexiting from the first lens and detecting scattered light reflected fromthe inspection target object.
 3. The scattered light detection module ofclaim 1, further including a transmitted scattered light detecting unitarranged inside a ring beam incident from the first lens and detectingscattered light transmitted from the inspection target object.
 4. Thereflected scattered light detection module of claim 1, wherein the firstlens includes a path changing unit for changing a path of the scatteredlight reflected from the inspection target object, and the reflectedscattered light detecting unit detects scattered light incident from thepath changing unit.
 5. The reflected scattered light detection module ofclaim 1, wherein the member is a hole, and the reflected scattered lightdetecting unit is disposed inside the hole.
 6. The reflected scatteredlight detection module of claim 1, further including: an additional lenschanging the angle of the terahertz Bessel beam incident from a Besselbeam forming unit to be smaller and to enter the first lens, theadditional lens is a second axicon lens, wherein the first lens is afirst axicon lens having the same shape as the second axicon lens andarranged to be symmetrical to the second axicon lens with respect to anaxis perpendicular to an optical axis.